what is the policy for the potential of personal property theft during the sitter's stay?

Here is the page explaining Rover's guarantee:

https://www.rover.com/us/guarantee/

Loss due to intentional or criminal acts, including theft are not covered by the Rover guarantee. Find a sitter who carries independent insurance coverage as many sitter do, and many offer theft coverage

No. Rover will not reimburse you for theft. Lock up your valuables and set up cameras if you worry about your property. Do not leave money, jewelry etc laying around. Put everything away.